Gas-phase interaction between nickel (II) and nitrobenzyl azides: An ESI-MSn study

Abstract

Organoazides are intermediates in the synthesis of imidometal complexes. Metalimido complexes have an important role in catalysis. Thus, the organoazide interaction with metals is an important issue. However, the isolation of organoazidometal complexes is difficult due to the easy loss of N2. The present study describes the complexation of nickel by nitrobenzyl azides by means of electro-spray ionization mass spectrometry (ESI-MS), which was used also as a probe for the characterization of isomers. Organoazidometal complexes were observed and isolated from solutions of NiCl2 and NiBr2 in methanol/water. A different solvent, ethanol/water was also used. The complexes detected were singly and doubly positively charged, with various stoichiometries. The most abundant species were [Ni(II)Az3]2+ for ortho- and para-isomers, and [Ni(II)Az3(H2O)]2+ for meta isomer, where Az stands for nitrobenzyl azides. The ortho isomer showed several single positively charged complexes integrating chloride as a ligand. The mass spectra of the three isomers allowed their differentiation based on different behaviour in the mass range m/z 296-m/z 312. The MS2 spectra of [Ni(II)Az3] 2+ were investigated aiming to characterize the three isomers but this analysis was not absolutely conclusive about the coordination site(s). Density functional theory calculations provided possible structures for the [Ni(II)Az3]2+ cation with the different isomers and their coordination modes could be responsible for their fragmentation pathways. © 2013 Elsevier B.V. All rights reserved.